Reflectivity is the fraction of incident radiation reflected by a surface. The reflectivity or anti-reflectivity of a coating typically depends on several different factors such as the type of material used, the index of refraction of the thin film materials, the thickness of the film, the number of layers and the differences in the materials used between multiple layers, and/or the micro morphology of the surface of the film.
Reflective films are used extensively on glass and other substrates where it is desirable to control the amount of light that passes through a substrate and/or impinges on the substrate. For example, windows on buildings are often coated with a thin film to reduce the amount of light that enters the building. Controlling the light transmission can improve the apparent quality of an image viewed through the window and can reduce the amount of heat produced from sunlight exposure, thereby reducing air conditioning demand in buildings.
Anti-reflective films are films that reduce the amount of light reflected off a surface and tend to cause light to be coupled into or through a substrate. Anti-reflective coatings have the generally opposite effect on light transmission as compared with reflective films.